The present invention relates to a process cartridge, an electrophotographic image forming apparatus using the same, and a separating mechanism for separating a developing member from an electrophotographic photosensitive drum. The present invention is particularly suitably usable with a color electrophotographic image forming apparatus.
The electrophotographic image forming apparatus forms an image on a recording material through an electrophotographic image formation type process. The electrophotographic image forming apparatus may be an electrophotographic copying machine, an electrophotographic printer (an LED printer, a laser beam printer or the like), an electrophotographic printer type facsimile machine, an electrophotographic printer type word processor or the like.
The process cartridge is a cartridge or unit which contains as a unit at least an electrophotographic photosensitive drum and developing means (developing member) and which is detachably mountable to a main assembly of an electrophotographic image forming apparatus.
In an image forming apparatus using an electrophotographic image forming process, a process cartridge type in which an electrophotographic photosensitive member and process means actable on the electrophotographic photosensitive member are contained as a unit in a process cartridge which is detachably mountable to the main assembly of the image forming apparatus, has been used. The process cartridge type is advantageous in that maintenance operations can be performed not by a service person but by the user in effect, and therefore, operability has been significantly improved. Therefore, the process cartridge type is widely used in the electrophotographic image forming apparatus.
As shown in FIG. 13, there is a color electrophotographic image forming apparatus 200 for a line type in which a plurality of process cartridges are arranged in a line. As for developing means for such cartridges, two types of structures are known. (1) A contact developing system in which the developing roller is kept in contact with the electrophotographic photosensitive drum in the developing operation, and (2) a non-contact developing system in which a predetermined gap is maintained between the photosensitive drum and the developing roller in the developing operation. In either of the types, a predetermined contact pressure or gap is maintained between the developing roller and the photosensitive drum during the developing operation, by urging the developing roller toward the photosensitive drum.
However, in the case of the cartridge of the contact developing system, the developing roller is press-contacted or urged to the photosensitive drum. In other words, an elastic layer of the developing roller is contacted to the photosensitive drum with a predetermined contact pressure. Therefore, if the cartridge is not operated for a long term with the cartridge being set in the main assembly of the image forming apparatus, there is a possibility of permanent deformation of the elastic layer of the developing roller. Because of this, the developed image can be non-uniform.
When the developing roller is not supplied with a bias voltage during the non-operation period (non-image formation), the toner on the developing roller may be deposited on the photosensitive drum. Such toner is liable to contaminate the recording material or the like.
In order to solve this problem, an image forming apparatus has been proposed in which when the image forming operation is not carried out, the developing roller is kept away from the photosensitive drum.
Accordingly, it is a principal object of the present invention to provide a process cartridge, an electrophotographic image forming apparatus and a separating mechanism for separating the developing member from the electrophotographic photosensitive drum, in which the developing member (developing roller, for example) is assuredly separated from the electrophotographic photosensitive member.
It is another object of the present invention to provide a process cartridge, an electrophotographic image forming apparatus and a separating mechanism for separating the developing member from the electrophotographic photosensitive drum, in which the developing member can be assuredly separated from the electrophotographic photosensitive member, and they can be brought into contact to each other with certainty.
It is a further object of the present invention to provide a process cartridge, an electrophotographic image forming apparatus and a separating mechanism for separating the developing member from the electrophotographic photosensitive drum, in which the developing member is assuredly separated from the electrophotographic photosensitive member except for the developing operation, and during the developing operation, the developing member is assuredly contacted to the electrophotographic photosensitive member with a predetermined contact pressure.
It is a further object of the present invention to provide a process cartridge, an electrophotographic image forming apparatus and a separating mechanism for separating the developing member from the electrophotographic photosensitive drum when the image forming operation is not carried out, and the developing member is assuredly contacted to the photosensitive drum during the image forming operation.
According to an aspect of the present invention, there is provided a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, comprising a first frame; a second frame coupled with the first frame for rotation about a shaft; an electrophotographic photosensitive drum provided in the first frame; a developing member, provided in the second frame, for developing an electrostatic latent image formed on the photosensitive drum with a developer; a developing member, provided in the second frame, for developing an electrostatic latent image formed on the photosensitive drum with a developer; an elastic member for applying an elastic force between the first frame and the second frame to urge the developing member to the photosensitive drum; a force receiving portion, provided downstream of the shaft with respect to a mounting direction in which the process cartridge is mounted to the main assembly of the image forming apparatus, for receiving a force from the main assembly of the image forming apparatus to keep the developing member away from the photosensitive drum when the process cartridge is mounted to the main assembly of the image forming apparatus; and a limiting portion for limiting upward movement of the first frame.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.